Continuous recovery method of adipic acid and diethyl adipate in monoethyl adipate synthesis process

Abstract

The invention belongs to the field of chemical separation, and particularly relates to a continuous recovery method of adipic acid and diethyl adipate in the monoethyl adipate synthesis process, which comprises the following steps: S1, rectification: a reaction mixture enters a rectification tower, the number of theoretical tower plates of the rectification tower is 30-50, the feeding position is 30-35 tower plates, and after rectification separation, the reaction mixture enters the rectification tower; extracting materials containing ethanol from the top of the rectifying still in sequence; a mixture containing the diethyl adipate and the adipic acid is extracted from a bottom liquid outlet of the rectifying tower; s2, recycling adipic acid: transferring a mixture containing the diethyl adipate and the adipic acid to a continuous extraction tower, extracting by an extraction agent, enabling an extracted water phase to enter a continuous stirring crystallizer, and cooling and crystallizing to obtain adipic acid solid; s3, recovery of the diethyl adipate: the extracted organic phase enters an alkalization reactor, and the pH is adjusted to 8-9 by an alkali liquor; the reacted solution enters a phase separator to be separated, a light phase obtained after phase separation enters a continuous extraction tower, a heavy phase obtained after phase separation is combined with an organic solution obtained after continuous extraction and enters a film evaporator, and vacuum concentration is performed to obtain a diethyl adipate product. The problems that in the monoethyl adipate production process, by-products such as adipic acid and diethyl adipate are high in energy consumption and low in recovery rate are effectively solved, the continuous recovery method of adipic acid and diethyl adipate in the monoethyl adipate synthesis process is provided, and the method has the advantages of being high in yield, high in product purity, stable in quality and low in energy consumption.

Description

Technical Field

[0001] The present application belongs to the field of chemical separation, and specifically relates to a method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate. Background Art

[0002] In the field of organic synthesis, in order to improve the utilization rate of raw materials and economic benefits, the effective recovery of by-products has always been an important topic. The esterification process synthesizes monoethyl adipate, that is, adipic acid and ethanol are reacted in solvents such as toluene, and dehydrated and esterified under the action of acid catalysts such as concentrated sulfuric acid and hydrochloric acid. In order to make the esterification reaction proceed, the chemical equilibrium reaction in the reaction system causes the hydrolysis and further esterification of monoethyl ester, so the reaction product contains by-products such as adipic acid and diethyl adipate. If these by-products cannot be effectively recycled, it will not only cause waste of resources, but also increase the cost of environmental protection treatment. With the popularization of green chemistry concepts and technological advances, how to efficiently and economically recover these by-products has become a research focus.

[0003] At present, common adipic acid and diethyl adipate recovery methods mainly include distillation, extraction, precipitation, etc. Although the distillation method is simple to operate, it requires a high operating temperature, the number of theoretical plates is relatively high, and the recovery efficiency is limited; the extraction method requires the selection of a suitable solvent, the operation is relatively complicated, and new waste liquid may be generated; the precipitation method is usually used in occasions where the purity requirement is not high, and the product quality is difficult to guarantee. Therefore, the existing adipic acid and diethyl adipate recovery technology generally has problems such as high energy consumption, high cost, and low efficiency, especially when facing a multi-component mixture, it is difficult to achieve an ideal separation effect. Therefore, it is urgent to develop an efficient recovery method with low energy consumption, high yield, and economic and environmental friendliness. Summary of the invention

[0004] In order to effectively improve the problem of high energy consumption and low recovery rate of by-products such as adipic acid and diethyl adipate in the production process of monoethyl adipate, the present application provides a continuous recovery method of adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate, which has the characteristics of high yield, high product purity, stable quality and low energy consumption.

[0005] The continuous recovery method of adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate provided in the present application adopts the following technical scheme: A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate, S1: distillation: the reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 30-50, the feed position is 30-35 plates, after distillation separation, ethanol-containing materials are successively taken out from the top of the distillation kettle; a mixture containing diethyl adipate and adipic acid is taken out from the distillation tower kettle liquid outlet; S2: Recovery of adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower. After extraction with an extractant, the extracted aqueous phase enters a continuous stirred crystallizer and is cooled and crystallized to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the alkali solution is used to adjust the pH to 8-9; the solution after the reaction enters the phase separator for separation, the light phase after phase separation enters the continuous extraction tower, the heavy phase after phase separation and the organic solution phase after continuous extraction enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration.

[0006] By adopting the above technical scheme, the present application uses the distillation residue of monoethyl adipate produced when adipic acid is dehydrated and esterified to synthesize monoethyl adipate under the action of concentrated hydrochloric acid catalyst as raw material, firstly through the method of reduced pressure distillation, by adjusting the theoretical number of plates and the feeding position of the pedal, a large amount of ethanol and soluble solvent impurities in the residue are efficiently removed, while ensuring the separation effect, taking into account the separation efficiency and reducing energy consumption. Too many plates will result in high energy consumption and low recovery efficiency, too few plates will result in low organic separation efficiency and low product purity; a mixed solution rich in diethyl adipate, monoethyl adipate and adipic acid is obtained at the bottom of the tower. A mixture containing diethyl adipate and adipic acid is passed into an extraction tower, and the aqueous phase after extraction is continuously stirred and crystallized to obtain adipic acid solid, which can be directly collected and reused; the mixture then passes through an organic phase into an alkalization reactor, and in an alkaline environment, the carboxylic acid in monoethyl adipate undergoes a neutralization reaction to generate a corresponding salt, which passes through a phase separator and is then used as a light phase, while the diethyl adipate that does not react with the alkali solution is efficiently separated as a heavy phase. In order to avoid the presence of incompletely precipitated diethyl adipate in the light phase, the light phase after phase separation is passed into an extraction tower for continuous extraction, so as to ensure that the diethyl adipate in the light phase after phase separation is completely extracted by the extractant, and the organic solution after continuous extraction and the heavy phase after phase separation are both entered into a thin film evaporator for concentration to obtain diethyl adipate solid, which is then recycled.

[0007] In a specific embodiment, the distillation operation is vacuum distillation, with a pressure of 80-130 Pa, a bottom temperature of 140-185° C., and a top temperature of 100-120° C.

[0008] By adopting the above technical solution and setting up reduced pressure distillation, the operating temperature is lowered, the use of high-temperature heating equipment is avoided, the destruction of high-boiling point compounds in the residual liquid by high temperature is avoided, the energy consumption is reduced, and the solvent with a lower boiling point can be recovered and utilized separately from the top of the tower.

[0009] In a specific possible implementation manner, the distillation further comprises a falling film heat exchanger for exchanging heat with the bottom of the distillation tower.

[0010] By adopting the above technical solution, a falling film heat exchanger is set up to allow part of the material to expand due to heat and partially vaporize, the density becomes smaller, and it leaves the vaporization space and countercurrently flows with the liquid phase, so that the temperature difference is maximized and the heat transfer efficiency is higher. Furthermore, through heat conversion, the overall energy consumption is greatly reduced and the product recovery rate is improved.

[0011] In a specific embodiment, the extractant includes one of cyclohexane, toluene, dichloromethane, carbon tetrachloride, ethyl acetate, and acetone.

[0012] In a specific embodiment, the volume ratio of the extractant to the mixture containing diethyl adipate and adipic acid is 1:(1.2-1.5).

[0013] By using a certain volume ratio of the extractant and the mixture containing diethyl adipate and adipic acid, on the one hand, the extractant can be wetted with the mixture containing diethyl adipate and adipic acid as much as possible, and on the other hand, water-soluble impurities can be reduced and the extraction effect can be improved.

[0014] In a specific embodiment, the stirring rate of the continuous stirring crystallizer is 600-800 r / min, and the cooling crystallization temperature is 0-5°C.

[0015] Under the action of stirring shear force, the adipic acid solute begins to crystallize. By adjusting the stirring rate, it is beneficial to the full crystallization of the solute, which is beneficial to faster growth of the crystal nucleus, more complete crystals, and reuse.

[0016] In a specific embodiment, the alkali solution in S3 is a 5-10% sodium carbonate solution.

[0017] By adopting the above technical scheme, a certain amount of sodium carbonate solution is added to react with monoethyl adipate in the organic phase, so that the carboxylic acid of monoethyl adipate is just neutralized, which can prevent the burden of wastewater treatment and reduce wastewater discharge on the one hand, and prevent excessive alkali solution from reacting with diethyl adipate to produce adverse side effects, thereby reducing the yield of the diethyl adipate product.

[0018] The operating pressure of the reduced pressure concentration is -0.07-0.09MPa, and the temperature is 130-150°C.

[0019] By reducing pressure and concentrating, it is ensured that the extractant is completely evaporated, so that the diethyl adipate product can be efficiently crystallized and recovered.

[0020] In summary, the present application includes at least one of the following beneficial technical effects: 1. The present application uses the distillation residue of monoethyl adipate produced by dehydration esterification of adipic acid under the action of concentrated hydrochloric acid catalyst as raw material, firstly through the method of reduced pressure distillation, by adjusting the theoretical number of plates and the feeding position of the pedal, a large amount of ethanol and soluble solvent impurities in the residue are efficiently removed, while ensuring the separation effect, taking into account the separation efficiency and reducing energy consumption. A mixed solution rich in diethyl adipate, monoethyl adipate and adipic acid is obtained at the bottom of the tower. A mixture containing diethyl adipate and adipic acid is passed into an extraction tower, and the aqueous phase after extraction is continuously stirred and crystallized to obtain adipic acid solid, which can be directly collected and reused; the mixture then passes through an organic phase into an alkalization reactor, and in an alkaline environment, the carboxylic acid in monoethyl adipate undergoes a neutralization reaction to generate a corresponding salt, which passes through a phase separator and is then used as a light phase, while the diethyl adipate that does not react with the alkali solution is efficiently separated as a heavy phase. In order to avoid the presence of incompletely precipitated diethyl adipate in the light phase, the light phase after phase separation is passed into an extraction tower for continuous extraction, so as to ensure that the diethyl adipate in the light phase after phase separation is completely extracted by the extractant, and the organic solution after continuous extraction and the heavy phase after phase separation are both entered into a thin film evaporator for concentration to obtain diethyl adipate solid, which is then recycled.

[0021] 2. By setting up a falling film heat exchanger, part of the material is expanded by heat and partially vaporized, the density becomes smaller, and it leaves the vaporization space and countercurrents with the liquid phase, so that the temperature difference is maximized and the heat transfer efficiency is higher. Then, through heat conversion, energy consumption is further reduced and product recovery rate is improved.

[0022] 3. By adding a certain amount of sodium carbonate solution to react with monoethyl adipate in the organic phase, the carboxylic acid of monoethyl adipate is neutralized, which can prevent the burden of wastewater treatment on the one hand, and prevent the excessive alkali solution from reacting with diethyl adipate and reducing the yield of the diethyl adipate product on the other hand. DETAILED DESCRIPTION

[0023] The raw materials in this application can be obtained from commercial sources.

[0024] Example 1 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 50, the feed position is at the 30th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 80 Pa, the bottom temperature is 140° C., the top temperature is 120° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.2. The aqueous phase after extraction enters a continuous stirred crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 96.3%.

[0025] Example 2 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 50, the feed position is at the 35th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 130 Pa, the bottom temperature is 185° C., the top temperature is 100° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.2. The aqueous phase after extraction enters a continuous stirred crystallizer, and the stirring rate is 800 r / min. The temperature is 0°C, and the adipic acid solid is obtained by cooling and crystallizing. S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5-10% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 150°C; the recovery rate of adipic acid and diethyl adipate reaches 96.1%.

[0026] Example 3 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 50, the feed position is at the 35th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 130 Pa, the bottom temperature is 140° C., the top temperature is 100° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.2. The aqueous phase after extraction enters a continuous stirred crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5-10% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.09 MPa and a temperature of 130°C; the recovery rate of adipic acid and diethyl adipate reaches 96.2%.

[0027] Example 4 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 30, the feed position is at the 30th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 80 Pa, the bottom temperature is 140° C., the top temperature is 120° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.2. The aqueous phase after extraction enters a continuous stirred crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 96.3%.

[0028] Example 5 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate, including the following steps: S1: distillation: the reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 50, the feed position is at the 30th plate, the falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 80 Pa, the bottom temperature is 140° C., the top temperature is 120° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture of diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.5. The aqueous phase after extraction enters a continuous stirring crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 96.4%.

[0029] Example 6 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 50, the feed position is at the 30th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 80 Pa, the bottom temperature is 140° C., the top temperature is 120° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction, wherein the volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1, and the aqueous phase after extraction enters a continuous stirring crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C, and the adipic acid solid is obtained by cooling and crystallizing; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 95.7%.

[0030] Example 7 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 50, the feed position is at the 30th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 80 Pa, the bottom temperature is 140° C., the top temperature is 120° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:2. The aqueous phase after extraction enters a continuous stirring crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH value is adjusted to 9 with 10% sodium carbonate solution. The solution after reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 96.5%.

[0031] Comparative Example 1 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 50, the feed position is at the 30th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 80 Pa, the bottom temperature is 140° C., the top temperature is 120° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.2. The aqueous phase after extraction enters a continuous stirred crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 10 with 35% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 94.3%.

[0032] Comparative Example 2 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 20, the feed position is at the 10th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, vacuum distillation is performed at a pressure of 80 Pa, the bottom temperature is 140° C., the top temperature is 120° C., and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.2. The aqueous phase after extraction enters a continuous stirred crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 93.7%.

[0033] Comparative Example 3 The method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: the reaction mixture enters a distillation tower, the theoretical number of the distillation tower plates is 50, the feed position is at the 30th tower plate, and the vacuum distillation is carried out at a pressure of 80 Pa, the tower bottom temperature is 140° C., the tower top temperature is 120° C., and the materials containing ethanol are successively taken out from the top of the distillation bottom liquid; a mixture containing diethyl adipate and adipic acid is taken out from the distillation tower bottom liquid outlet; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.2. The aqueous phase after extraction enters a continuous stirred crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 94.9%.

[0034] Comparative Example 4 A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate comprises the following steps: S1: distillation: a reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 50, the feed position is at the 30th plate, a falling film heat exchanger performs heat exchange on the bottom of the distillation tower, and at the same time, atmospheric distillation is performed, the bottom temperature is 140°C, the top temperature is 120°C, and ethanol-containing materials are sequentially extracted from the top of the distillation bottom; a mixture containing diethyl adipate and adipic acid is extracted from the bottom liquid outlet of the distillation tower; S2: Recovering adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower, and toluene is added for extraction. The volume ratio of toluene to the mixture containing diethyl adipate and adipic acid is 1:1.2. The aqueous phase after extraction enters a continuous stirred crystallizer, and the stirring rate is 600 r / min, and the temperature is 5°C for cooling and crystallization to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the pH is adjusted to 8 with 5% sodium carbonate solution. The solution after the reaction enters the phase separator for separation, and the light phase after phase separation enters the continuous extraction tower. The heavy phase after phase separation and the organic solution phase after continuous extraction for 3 times enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration at a pressure of -0.07 MPa and a temperature of 130°C. The recovery rate of adipic acid and diethyl adipate reaches 92.1%.

[0035] The implementation of this application and the comparative example realize the continuous and efficient recovery of adipic acid and diethyl adipate through the ingenious cooperation of a series of separation means such as distillation, extraction crystallization, alkalization phase separation, extraction concentration, and the recovery rate of the embodiment is as high as more than 95%. The whole process embodies the characteristics of green chemistry, and adopts energy-saving and environmental protection measures such as vacuum distillation combined with falling film heat exchanger, so that the overall energy consumption of the embodiment is reduced by 30%, the wastewater discharge is reduced by 50%, and the product quality is stable, which meets the various quality index requirements of downstream customers for adipic acid and diethyl adipate, and has good market competitiveness.

[0036] Compared with Example 2, Example 1 has a lower theoretical plate number. The higher the pedal height, the worse the separation is. The low boiling point solvent and impurities cannot be completely separated, resulting in more impurities in subsequent operations, undesirable reactions, and a lower product recovery rate. Comparing Example 1 with Example 8 and Comparative Example 1, it can be seen that during the alkalization of the organic phase after extraction, diethyl adipate reacts with the alkali solution with too high alkalinity, reducing the recovery rate of the diethyl adipate product. Comparing Example 1 with Example 6, within the ratio of the extractant disclosed in the present application and the mixture containing diethyl adipate and adipic acid, the extraction and separation effect is better and the recovery rate is high. This may be based on the higher solubility and extraction selectivity of toluene. The content is too low to completely extract the product, affecting the recovery rate of diethyl adipate. Comparing Example 1 with Comparative Examples 3-4, the falling film heat exchanger exchanges heat with the distillation tower kettle, and the vacuum distillation can improve the recovery rate of adipic acid and diethyl adipate.

[0037] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate, characterized in that: The method comprises the following steps: S1: distillation: the reaction mixture enters a distillation tower, the theoretical number of plates of the distillation tower is 30-50, the feed position is at 30-35 plates, after distillation separation, ethanol-containing materials are successively taken out from the top of the distillation kettle; a mixture containing diethyl adipate and adipic acid is taken out from the distillation tower kettle liquid outlet; S2: Recovery of adipic acid: The mixture containing diethyl adipate and adipic acid is transferred to a continuous extraction tower. After extraction with an extractant, the extracted aqueous phase enters a continuous stirred crystallizer and is cooled and crystallized to obtain adipic acid solid; S3: Recovery of diethyl adipate: The organic phase after extraction enters the alkalization reactor, and the alkali solution is used to adjust the pH to 8-9; the solution after the reaction enters the phase separator for separation, the light phase after phase separation enters the continuous extraction tower, the heavy phase after phase separation and the organic solution phase after continuous extraction enter the thin film evaporator, and the diethyl adipate product is obtained by reduced pressure concentration.

2. The continuous recovery method of adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate according to claim 1, characterized in that: The distillation operation is vacuum distillation, the pressure is 80-130pa, the bottom temperature is 140-185°C, and the top temperature is 100-120°C.

3. The continuous recovery method of adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate according to claim 1, characterized in that: The distillation further comprises a falling film heat exchanger for exchanging heat with the bottom of the distillation tower.

4. The method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate according to claim 1, characterized in that: The extractant includes one of cyclohexane, toluene, dichloromethane, carbon tetrachloride, ethyl acetate and acetone.

5. The method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate according to claim 4, characterized in that: The volume ratio of the extractant to the mixture containing diethyl adipate and adipic acid is 1:(1.2-1.5).

6. The method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate according to claim 1, characterized in that: The stirring rate of the continuous stirring crystallizer is 600-800 r / min, and the cooling crystallization temperature is 0-5°C.

7. The method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate according to claim 1, characterized in that: The alkali solution in S3 is 5-10% sodium carbonate solution.

8. The method for continuously recovering adipic acid and diethyl adipate in the process of synthesizing monoethyl adipate according to claim 1, characterized in that: The operating pressure of the reduced pressure concentration is -0.07-0.09MPa, and the temperature is 130-150°C.